1. Field of the Invention
The present invention relates to an LC composite component, that is, an electronic component including an inductor and a capacitor.
2. Description of the Related Art
There are high demands for reductions in size, thickness and cost of wireless communication apparatuses such as cellular phones and wireless LAN communication apparatuses. Accordingly, electronic components for use in such wireless communication apparatuses are expected to meet the same demands. Furthermore, high electromagnetic shielding performance is demanded of such electronic components because they must be contained within a narrow space in a wireless communication apparatus.
An example of electronic components for use in wireless communication apparatuses is an LC composite component including an inductor and a capacitor. A known technique for downsizing an electronic component including an inductor is to surround the inductor with a material having magnetism, as disclosed in JP H07-135403A, JP 2002-052644A, and JP 2008-027982A, for example. This technique allows for a reduction in the size of the inductor needed to obtain a desired inductance, and consequently allows for downsizing of the electronic component.
JP H07-135403A discloses a high frequency filter in which a ground electrode is formed on one surface of a dielectric substrate, a plurality of pattern electrodes for forming microstrip resonators are formed on the other surface of the dielectric substrate, and a magnetic substrate is formed on the plurality of pattern electrodes.
JP 2002-052644A discloses an electronic component formed of a stack of constituent layers and conductor layers, each of the constituent layers being formed by coating a glass cloth with a resin that contains dielectric material powder and one of magnetic material powder, dielectric-coated metal powder and insulator-coated magnetic metal powder.
JP 2008-027982A discloses an LC composite component including a first magnetic substrate, a capacitor layer formed on the first magnetic substrate, an inductor layer formed on the capacitor layer, a second magnetic substrate formed on the inductor layer, and a magnetic core member. The capacitor layer includes lower electrodes formed on the first magnetic substrate, a thin dielectric film covering the top surfaces of the lower electrodes, and upper electrodes placed opposite to the lower electrodes with the thin dielectric film in between. The inductor layer includes a coil conductor formed on the top surface of an insulating layer. The magnetic core member passes through the inner diameter of the coil conductor and connects the first magnetic substrate and the second magnetic substrate.
A typical approach to enhancing the electromagnetic shielding performance of an electronic component is to provide two metal layers each having a large surface area on opposite sides of a constituent part of the electronic component, particularly an inductor. If this approach is applied to an LC composite component, however, any attempts to reduce the thickness of the LC composite component would lead to a reduced distance between the inductor and each metal layer, which would in turn lead to increased losses of the inductor due to eddy current losses, and eventually lead to degraded characteristics of the LC composite component in high frequency bands.
JP H07-135403 A teaches that the high frequency filter disclosed therein can achieve a greater reduction in size compared with a conventional high frequency filter which uses no magnetic substrate, and further, this high frequency filter is inexpensive because the magnetic substrate provides a shielding effect and thus eliminates the need for a shield electrode or the like.
In the high frequency filter disclosed in JP H07-135403A, however, all the plurality of pattern electrodes having inductance components and realizing a capacitor are placed on one plane. It is therefore difficult to achieve a further reduction in size. Furthermore, any attempts to achieve reduction in thickness of this high frequency filter would lead to a reduced distance from the pattern electrodes to the ground electrode having a large surface area. This would in turn lead to reduced inductance components of the pattern electrodes, thus making it difficult to obtain desired characteristic impedances of the pattern electrodes. It is thus difficult to achieve a further reduction in thickness of the high frequency filter disclosed in JP H07-135403A.
The electronic component disclosed in JP 2002-052644A uses a large amount of magnetic material powder, dielectric-coated metal powder or insulator-coated magnetic metal powder because every constituent layer of the electronic component contains one of such powders. This raises the cost of the electronic component. Further, in this electronic component, an inductor-forming conductor layer and a capacitor-forming conductor layer are disposed to overlap each other with a constituent layer in between when viewed in a direction perpendicular to the planes of the plurality of constituent layers. Thus, any attempts to reduce the thickness of this electronic component would lead to a reduced distance between the inductor-forming conductor layer and the capacitor-forming conductor layer, which would in turn lead to increased losses of the inductor due to eddy current losses, and eventually lead to degraded characteristics of the electronic component in high frequency bands.
The LC composite component disclosed in JP 2008-027982A has two magnetic substrates and thus uses a large amount of magnetic material, which raises the cost of the LC composite component. Further, in this LC composite component, the capacitor layer and the coil conductor are disposed to overlap each other with the insulating layer in between when viewed in a direction perpendicular to the planes of the magnetic substrates. Thus, any attempts to reduce the thickness of this LC composite component would lead to a reduced distance between the capacitor layer and the coil conductor, which would in turn lead to increased losses of the coil conductor due to eddy current losses, and eventually lead to degraded characteristics of the LC composite component in high frequency bands.